When products are used up, they become waste products. Hitherto, these waste products have been collected, burnt up if necessary and treated by dumping the resulting residue in a landfill. Metals such as iron and copper, waste papers as well as rag have always been recycled and utilized. As a result, the waste products discarded as rubbish were only raw garbage from a kitchen mainly.
However, new materials, which were not an object of recycling, have recently been produced, supplied and utilized. The representative material is plastics.
For the purpose of the improvement of design, weight saving, price-reduction and the improvement of insulation properties of a product, plastics have been used as a housing, casing materials, component parts and cushioning materials in the product in various fields, for example in a wide variety of applications such as household appliances, products such as information processing equipments or communication equipments, automobiles and building materials. As a result, these plastics result a large amount of waste materials after used, but the most of the waste plastics have been treated by dumping them in a landfill or burning them up under the present circumstances.
As a countermeasure proposed for treating the waste plastics, for example, there is a technique as described in Japanese patent application Laid-Open Publication 7-203744. The technique described in this patent application Laid-Open comprises placing alternatively a refractory, non-acidic and porous particulate material and waste plastics as a stack into an incinerator and burning them to carbonize or incinerate the waste plastics.
However, the production of plastics further increases continuously and a wide variety of plastics are now produced at the level of about ten million ton for the year. In local governments, when such useful plastics reaches a stage to be treated as wastes, the treatment of the waste plastics has become a problem.
The waste plastics have been reused or recycled but parts of the used plastics have been only reused.
It can be said that the reason is because the deterioration in physical properties of plastics due to the change in properties with time during use, the contamination on recycling, the heat history and others makes recycling of plastics very difficult. However, since global environmental problems has become recently into the limelight, there is an eager demand for a technique utilizing effectively these used plastics in view of the effective utilization of limited resources, the waste problem, the generation of harmful gases or dust and others.